import React, { Component, Fragment } from 'react'
class Child extends Component {
  shouldComponentUpdate () {
    return false 
  }
  render () {
    console.log('render child')
    return (
      <Fragment>
        child
      </Fragment>
    )
  }
}
export default class App extends Component {
  state = { 
    count: 100
  }
  render() {
    return (
      <div>
        <button onClick = { () => {
          this.setState({
            count: this.state.count + 1
          })
        }}>加</button>
        <Child />
      </div>
    )
  }
}
